Advances in polymerization and catalysts have produced new polymers having improved physical and mechanical properties useful in a wide variety of products and applications. With the development of new catalysts, the choice of polymerization, such as solution, slurry, high pressure, or gas phase, for producing a particular polymer has been greatly expanded. Advances in polymerization technology have also provided more efficient, highly productive and economically enhanced processes.
Metallocene catalyst components have been widely used to produce polyolefins such as polyethylene polymers. They have provided efficient processes and a variety of new and improved polymers. In addition, catalyst systems have also been used that comprise more than one catalyst component, in effect, providing more than one active site to polymerize monomers during the polymerization process. Catalyst systems comprising two or more different catalyst components have been used, for example, to produce multimodal polymers. However, there is continued focus in the industry on developing new and improved catalyst systems. Some have focused on designing the catalyst system to produce new polymers, others on improved operability, and yet others on improving catalyst productivity. The productivity of a catalyst can be an important concern for polyolefin producers.
A number of methodologies used for delivering catalysts to reactors require the catalyst to be supported on an inert carrier such as silica. Impregnating a catalyst on a support has often been found to cause a significant decrease in catalyst activity. In addition, large particles (>25 micrometers) of the support material have frequently been found in the finished polymer product. These particles may adversely affect polymer properties. This has been observed in film applications where unexploded silica particles appear as defects or gels. Spray-drying techniques have been employed as an alternative to supported particles. Once a catalyst system has been spray dried, the spray-dried catalyst system may be added to a diluent to form a catalyst slurry and pumped to a polymerization reactor.